Expansion engine



l\{oy. 24, 1953 Ryw. HUGHES 2,660,154

EXPANSION ENGINE Nov. 24, 1953 R. w. HUGHES EXPANSION ENGINE 4Sheets-Sheet 2 Filed Sept. 2l 1951 Y a M. MJ .w ,a M w@ VCL j a Mx 1 uaf a .2, 4 M Y 0 w W 2-/ A f/ 7|/ um aww H 7 i Arrow/fr Nov. 24, 1953 R,w HUGHES A2,660,154

EXPANSION ENGINE Filed Sept. 21, 1951 4 Sheet s-Sheet 3 ATTP/VEY NOV 24,1953 R. W. HUGHES EXPANSION ENGINE 4 Sheets-Sheet 4 Filed Sept. 21 1951Patented Nov. 24, 1953 UNIT ST EXPANSIN ENGINE Application September 21,1951, Serial No. 247,731

Claims. 1

This invention relates to an expansion engine, especially to anexpansion engine of the reciprocating piston type.

The commercial production of oxygen for in dustrial uses may beaccomplished in a number of different ways, one of these being disclosedand claimed in the copending patent application Serial No. 236,014, ledJuly 10, 1951, which is the invention of Samuel C. Collins, and is as'-signed to the assignee of this invention. The

method and apparatus therein disclosed and claimed for the production ofoxygen involves providing a substantial quantity of refrigeration. Thenecessary refrigeration is desirably provided by expanding the air,after the removal of impurities, with the performance of external work,such expansion conventionally taking place in an expansion engine. Myinvention relates 'to an improvement in an expansion engine for use inapparatus for the separation of gases such as disclosed and claimed inthe above identified patent application of Dr. Collins.

The extremely low temperatures encountered in the separation of air intoits components presents numerous design problems, one of which involvesthe diliculty of packing an engine of conventional design. It will ofcourse be appreciated that ineicient packing will result in blow-by ofcold air, involving a serious loss of refrigeration.

It is accordingly an object of this invention to provide an expansionengine adapted to low temperature operation and requiring a minimum ofrod packing, and further requiring a minimum pressure differential whererod packing is necessary. in an expansion engine in which valve push-rodpacking is entirely eliminated, and in which the piston rod packing issubject to expansion engine exhaust pressure instead of inlet pressurewhereby the pressure dilierential across the packing is materiallyreduced and whereby the loss of valuable refrigeration is eliminated.

In the drawings:

Fig. 1 is a longitudinal sectional view through the cylinder of anexpansion engine made according to this invention, but not showing thecrankshaft, connecting rod, and crosshead, which are conventional. riheparts are shown in this gure in their relation with the piston at topdead-center, showing the admission valve in the process of opening.

Fig. 2 is a View similar to Fig. 1, but with the admission valve shownin its wide open position.

Fig. 3 is a view similar to Fig. l but showing the parts in position tobegin cut-off-ie., closing of the admission valve.

This and other objects are accomplished Fig. 4 is a view similar to Fig.1, but showing the parts in their relationship with the admission valvecompletely closed-i. e., cut-oli is complete and expansion is ready tobegin.

Fig. 5 is a View similar to Fig. 1, but showing the parts in theirrelationship in which the exhaust valve is wide open, and the piston isat bottom dead center.

Figs. 6, 7 and 8 are views in section substantially on lines 8 6, 1 1and 8 8 respectively of Fig. 1, with the qualification that Fig. 8, forsimplication, is shown without the cylinder head clamping sleeve.

Fig. 9 shows a modified resilient device to permit long or shortcut-ofi.

In 'an expansion valve made according to this invention and shown in thedrawings, there is provided a cylinder 2 having the usual highlypolished bore ll. The piston 6 having a plurality of piston rings 8 isreciprocably mounted in the cylinder 2. An end-wall l@ is provided forone end of the cylinder 2. A piston rod l2 is secured to the piston 6 inany suitable manner, as for example by means including a threaded memberI4. The piston rod l2 extends outward through the opposite end of thecylinder.

The aforesaid opposite end of the cylinder 2 is closed off by a lowerendwal1 l5, to which there is secured an exhaust chamber i8. Exhaustchamber I8 preferably comprises a pair of cylindrical sleeves 2li and 22Vsecured to the lower endwall Iii in any suitable manner and deiining anannular space between them which is sealed off by a toroidal head 2lisecured to the two sleeves 20 and 22. Openings 2t are spaced around thepiston rod l2 in the lower end-wall I6 in order to connect the interiorof cylinder 2 with the chamber I8. A suitable conduit 28 is connectedwith the exhaust chamber I8 to conduct expansion engine exhaust awayfrom the engine.

An inlet surge chamber 3! is provided at said one end of the cylinder,and consists of a cylindrical member 32 closed at its upper end by acover plate 3i and secured at its lower end to the lirst named end-wallli! in any suitable manner, as for example by a flange 38 secured to thelower end of the cylindrical member 32, flange 36 in turn being securedto end-wall l0 by threaded members 33.

I provide means to admit fluid under pressure to the interior of thecylinder 2 through the endwall I il. To this end, a port lil is providedin the end-wall; port li has a valve seat i2 which cooperates with asimilar seat on a port closure 44. The port closure M is movable intoportopen and port-closed positions, being guided in its movement by aport closure operator indicated generally at 46. The port closure 44 ispreferably a hollow plug-like member having a projection 48 at one endand having secured to its other end a tubular member 50 which forms apart of the port closure operator 46. The projection end of the interiorof closure 44 is threaded to receive a hollow nut 52 which extends upinside the tubular member 50, whereby the tubular member 50 is heldbetween one end of nut 52 and port closure 44.

Tubular member 50 extends substantially throughout the surge chamber 30;in fact, tufbular member 50 extends out through the end cap 34 into acylindrical cap or sleeve 54. Cylindrical cap 54 is secured in anopening 56 in the end cap 34, and at its other end is plugged, as shownat 58. Tubular member 50 is similarly plugged as shown at 60.

Detent means indicatedv generally at 62 are provided to hold the portclosure operator and the port closure in one of its operating positions;in the embodiment shown the operating position is the port-openposition. The detent means has `a member which is associated with thesurge chamber cylindrical member 32 and another member which isassociated with the port closure operator 46. Thus, between the upperend of cylindrical member 32 and the end cap 34, there are provided theballs of a ball detent. More specifically, a plate member 64 is providedwith an annular shoulder 66 whereby it is secured in any satisfactorymanner to the upper end of cylindrical member 32, and threaded members68 secure the end cap to the plate member 64.

Radial flange is made integral with the plate member 64, and balls 'l2are held between the radial flange I0 and the inner face 14 of the endcap 34. The balls 'l2 are biased radially inward by means of a garterspring 16 acting against arcuate members 18. See especially Fig. 6 forthis detail. The other portion of the detent consists of a groove 80 inthe periphery of a bushing 82. Bushing 82 is secured to and moves withthe tubular member 50 of the closure operator 46.

Bushing 82 has a sliding tin a bore 84 provided in the end cap 34; Thefit of bushing 82 in bore 84 forms part of guide means for the closureoperator 46. Additional guide meansare provided by the fact that tubularmember 50 has a telescoping fit in cylindrical cap or sleeve 54. Thus,the end cap assembly provides guide means to center the closure operator46 as it guides closure 44 between its port-openand port-closedpositions.

The piston 6 is provided with at least one axial passage for thewithdrawal of spent air or exhaust away from the expansion engine.Preferably, numerous exhaust passages 86 are provided through the pistonthroughout its length, these passages being substantially parallel withthe cylindrical axis of the piston. Seev especially Fig. 8 for thisdetail.

A closure 88 is provided for the axialpassage or passages. The uppersurface of the piston has a seat 90 which cooperates with a surface onthe closurel 88 to seal the upper openings of the passages 86. Closure88 is movable into passageopen and passage-closed positions, being shownin its passage-closed position in Figs. 1-4, and in its passage-openposition in Fig. 5. A passage closure operator indicated generally at 92is provided to guide the passage closure in its movement between theopen and closed positions. As a part of the closure operator 32, thereis provided a rod 34 having a stepped diameter at its lower end, ofwhich the small diameter portion SE extends through a projection 08 onthe closure 88. A shoulder |00 is formed at the junction of the smalldiameter portion 96 and the larger portion of the rod, and theprojection 98 is clamped between the shoulder |00 and a nut |82. Theprojection 88, small diameter portion 66 and nut |02 are all received ina centrally located bore or recess |04 in the upper face of the piston6.

lt will be noted that the rod 94 telescopes inside the tubular member 50and inside the hollow nut 52. Near its lower end, rod 94 is providedwith flats |06 to receive a suitable wrench in order that rod 94 may beheld against turning when the nut |02 is applied. Also near its lowerend, rod 94 ts in a recess 0r bore |08 in the closure 83, and in theannular space between bore |58 and rod 94 there is placed a coil springH0, which acts at its one end against closure 88 and at its other endagainst nut 52 and therefore closure 44. i

At its upper end, rod 94 is provided with a large diameter portion ||2which may if desired be a sleeve slipped over` the end of the rod andsecured thereto. Sleeve ||2 has a sliding lit in the tubular member 50,and, along with the t of projection 98 in the 'bore |04, provides guidemeans for the closure operator 92 to guide it in its movement. At itslower end, the large diameter portion ||2 carries a cam surface ||4 anda shoulder H6. The shoulder ||6 is adapted to cooperate with the portclosure 44, and more specifically with the nut 52 which is screwed intothe port closure 44 to become a part thereof.

The cam surface ||4 is part of a device to disengage the detentmechanism 62. Also included in the means to disengage the detent 62 isthe resilient device indicated generally at ||8. The resilient device H8comprises a disc |20 which is preferably integral with bushing 82. Disc|20 f has several stepped radial bores here 'shown as four in number(Fig. 7) as indicated at |22. In each bore |22 there is provided a ball|24 backed up by a pressure plate |26. A spring |28 in each bore iscompressed between pressure plate |26 and a plug |30. It will be notedthat the portion of the bore in which the ball lies is large enough toaccommodate the ball and to permit free radial movement of the ball, andthat the portion of the bore in which the pressure plate and the springlie is a little larger in order to provide a shoulder to limit theradially inward movement of the pressure plate |26. The portion of thebore in which the plug |30 is situated is still larger and is threaded.Thus the threaded plug |30 is turned inward until it engages theshoulder provided by the juncture with the next smaller size portion ofthe bore |22.

Detent means are also provided to hold the passage closure in oneoperating position, which in the embodiment shown is the open position,as seen in Fig, 5. To that end, a shoulder is provided on the projection98. This shoulder takes the form of a conical surface |32 which isopposed by another similar conical surface |34 on a resilient pressureplate |36. Balls |38 are located in the annular space between the twoconical surfaces |32 and |34. A spring |40 biases the pressure plate |36against the balls |38. Balls |38 are adapted to cooperate with a groove|42 provided in the cylindrical wall of the recess |84.

Referring again to the expansion engine cylinder more generally, it maybe pointed out that the cylinder heads or end-walls |0 and I6 may beheld in engagement with the cylinder 2 in any suitable manner, but apreferred method of holding the cylinder heads or end-walls I0 and I6and the cylinder 2 together, as shown in Fig. 1, comprises a clampingsleeve |44 which is preferably provided in two parts so that it mayreadily be placed around the cylinder 2 and the end-walls I0 and I6. Thetwo-part sleeve |44 is secured at its one end to a ring |48 which is ofcourse also split, and at its upper end to a ring |48. Ring |48 issimilarly provided in two parts. The lower split ring |46 engages thelower cylinder head or end-wall I8 while the upper split ring |48 isengaged by a split collar |50. Collar |50 carries clamping screws |52which engage the upper surface of the end wall or upper cylinder headl0.

The piston rod |2 may be packed in any suitable conventional manner andis preferably packed at some point remote from the cylinder, preferablyas far from the cylinder as possible. The packing may be conventionaland is not shown here.

Reference is now made to Fig. 9, wherein is shown a modilication of theresilient device to permit short cut-off or long cut-olf. In Fig. 9, aresilient device |80 takes the place of device ||8 of the firstembodiment. In the device |60, one set of balls |62 is provided toeffect short cutoff, and another set of balls |84 permits long cutoi.

Each of balls |82 is biased radially inward by a spring |86 which isencased in a bellows |88.

Operation Referring again specifically to Fig. 1, the piston is shown ashaving just reached top dead center. I

Just before it reached this position, the port closure 44 was closed, aswas also the passage closure 88. As the piston approaches top deadcenter, the upper surface of passage closure 88 engages the projection48 of closure 44 and cracks or opens slightly the port closure 44. Thisis the position shown in Fig. l.

With the port closure 44 open as shown in Fig. 1, air at the inletpressure in the inlet surge chamber 80 is able to enter the upper end ofthe cylinder through the small clearance provided between port closure44 and seat 42. With inlet pressure now applied to the under side ofport closure 44, the force of spring ||0 is suiiicient to move the portclosure 44 the rest of the distance into wide open (port-open) position,shown in Fig. 2, in which the detent mechanism 62 is engaged, i. e.,balls 12 engage the groove 80. Air under pressure thereupon flows intothe cylinder through the port 40, moving the piston 6 downward. Inletpressure is of course applied to the upper face of the passage closure88, holding closure 88 firmly on its seat 90. Consequently, as piston 6moves downward under the influence of the compressed air operating onits upper surface,

pressing springs |28.

it carries the passage closure operator 92 along with it. As closureoperator 92 moves downward, inside the tubular member 50, the camsurface |4 moves from the position shown in Fig. 2 to the position shownin Fig. 3 in which it is in engagement with the resilient device H8.This is the point of travel of the piston at which cut-off begins. Thesprings |28 are heavy enough to hold balls |24 in contact with the camsurface I4 so as to disengage balls 12 from their cooperating groove 80.Continued movement downward of the piston 6 eventually completely closesthe valve or closure 44, moving the valve from the position shown inFig. 3 to the position shown in Fig. 4.

Continued downward movement of piston 6 brings about expansion of theair in the cylinder. The external work which is performed during thisexpansion is done at the expense of the internal energy of the air, sothe air temperature is reduced. It should be noted that as the piston 6moves downward from the position seen in Fig. 4, closure 88 moves downwith it, requiring that balls |24 ride up on the cam ||4, com-Thereafter, the balls |24 ride on the large diameter surface of theportion ||2.

As the piston 6 continues its downward movement, eventually the shoulder||6 on the passage closure operator 92 engages the upper end of nut 52.With port closure 44 already in its fully closed position, any furtherdownward movement of the piston 6 must result in relative movement ofthe piston 6 and passage closure operator 92. This relative movement canin turn come about only by opening the passage closure 88. Accordingly,in the short distance that the piston moves from the time that shoulder||6 engages the upper end of nut 52 until piston 6 reaches bottom deadcenter, exhaust valve or passage closure 88 opens to uncover the upperends of passages 86 in the piston 8. As the piston reaches bottom deadcenter, the balls |38 of the passage closure detent engage theircooperating groove |42 provided in the wall of recess |04 of the piston.

With the passage closure detent means engaged, the passage closure 88remains in passageopen position as the piston moves upward. The passageclosure 88 remains open until the upper surface of passage closure 88engages the lower end of projection 48. Further upward movement of thepiston causes the projection 48 to force the balls |38 out of theircooperating groove, closing the valve or passage closure 88. Stillfurther upward movement of the piston opens the admission valve or portclosure 44 as -described above, and the cycle repeats.

The operation of the embodiment of Fig. 9 will now be discussed. Forshort cut-off, valve |82 is set to connect conduit |18 with conduit |86.This is done by turning the valve clockwise through 90 from the positionshown in Fig. 9. With conduits |18 and |88 connected, the pressure onthe plates |10 is the same on both sides, and the springs |86 areoperative. In consequence, the balls |82 eifect cut-olf as explainedabove.

After balls |82 ride up on the cam surface H4 and are pressed againstthe large diameter portion ||2, continued movement downward of rod 94'causes balls |84 also to ride up on the cam surface, and balls |84 haveno eiect on cut-off.

With valve |82 in the position shown, the presassunse 7 sure:differential. acrossplates f l 1.0 will `bias them outward so thatballs.162 vwillfnot effect cut-off. BallsirllM-then operate to bring aboutlong cuto-i. e., cut-oli after a longer'period ofadmission ofihighpressureair.

Itrwill be evident to those skilled in the Vart that 'I have hereprovided an expansionengine of greatly improved f design, in which novalve push-rodsextend Vthrough walls 'whichseparate chambers atdifferent pressures. Accordingly, no valve push-'rod packing is requiredand 'the losses :always present with. faulty packing are thereby greatlydiminished, as the only rod packingrrequiredis that needed forthe'piston'rod. Another advantage inherent in my improved designistheshort distance `oftravel ofthe valves hereinabove called closures Otheradvantages -Will be apparentto those skilled in the art.

While there are in this application specifically described -two forms4Vwhich the invention may assume in practice, it will be understood thatthoseforms of the same are shown for purposes 0f `illustration, andthatv the invention may be modified and embodied in various otherl formsWithout departing from its spirit or the scope of the.- appended claims.

I claim:

1. :In anexpansion engine,-a cylinder, an end wall for the cylinder andhaving a port, a closure @forthe pcrt,apiston having at least one iaxial passage and reciprocably mounted inthe cylinderfa closure for theaxial passage, a closureioperator for-the port closure, anotherAclosurez-.foperator forl the passage closure, detent means:associatedrwith the. port lclosure operator tor'holdit in port-openposition,.other detent means associated with the passage closureoperator'tolhold' it inpassage-open position, means to :disengage` thefirst-named'detent means and close the port; and means to -disengagesaid other detentimeans Vand close the passage.`

2. `An vexpansion engine as in claim 1, in which one closureoperatortsinside and is reciprocable with respect yto the other, theiirst-nameddetent'- disengaging. means .including a shoulder provided i on theinside closure operator.

3. An expansion engineas in claim 1, in which theksecond-'nameddetent-disengaging means in- `cludessa :projection on the port closureadapted tosbeengaged by thepassage closure.

V4.An `expansionengine as in .claim 3, in which the'vrecessisfcentrallylocated in the high pressure'endof the piston.

5.2 Ari lexpansionv engine as in claim 1, 'in which oneclosure operatoriits inside and is reciprocable withrespect to'thezother, theiirst-nameddetent- -disengaging means including a resilient device :positonsaclosure operator for the port closure,

another closure operator for the'passage closure, meanscooperable withthe port closure to move the-'passage closure into passage-openposition, means cooperable with the passage closure to Ymove :thefportclosure into port-open position,

detent :means associated with the l port closure operator to hold itimport-open positionfother detent means associated with the passageclosure operator to hold it in Ipassage-open position, means todisengage the first-named detent means and eiect'movement of thel portclosure to portclosed position, and means'to disengage said otherdetent'means and effect movementlof the passage closure intopassage-closed position.

8.. Anexpansion engine as in claim 7, in which one closure operator fitsinside and is reciprocable with respect to the other, the rst-namedmeans including a shoulderprovided on the inside closure operator.

9. 'An expansion engine as in claim 8, in'which the second-named'meansincludes 'a projection on the port closure adapted to be engaged by thepassage closure.

10. An expansion 'engineas in claim 9, in which thenieans to disengagethe 'Iirst detent means includes a resilient device cooperable withitheinside closure operatorl 11. An expansion engine asin claim 10, in whichthe meansto disengage saidother -detent means includes the aforesaidprojectionvon the port closure.

12. An expansion engine asin claim 11, in which the piston'is providedwith a recess having a groove, said other detent means including thegroove.

13.` An expansion engine as inclaim 12, in which the recess is centrallylocated inthe high pressure end of the piston, and in which the passageclosure operator includes a member which extends into the recess.

14. `An expansion engine-as in claimY 7, in which the second-namedmeans-includes a projection on the'port closure adapted to befengagedbythe passage closure.

15. `An expansion engine as :in claimde, in which the means-toAdisengage the first detent means includes a resilient device cooperablewith the inside closure operator.

16. An expansion engine as in claim 15, in which the means to disengagesaid lother detent means includes the aforesaid projection on the portclosure.

17. An expansion 'engine'as in claim '7, in which the pistonis providedwith a recess having a groove, said .other detent means including thegroove. f

18. Y*An expansion engine as in claim 1'7, in which the recess iscentrally located in the high pressure end of the piston, and in whichlthe passage closure operator. includes a member which extends intotherecess.

19. In a reciprocating expansion engine: a cylinder; a cylindrical inletsurge chamber adjacent one end of the cylinder and co-axial therewith;an end wall for said one-end of vthe cylinder-and separating the surgechamber and the cylinder interior; an exhaustchamber at the other endofthe cylinder; a piston reciprocably mounted in .thefcylinder and`having at least one` axial passage therethrough; Va piston rod securedto thepiston an'dextending out through said other end. 'of the cylinder;means to admit an elastic fluid from the surgechamber'to the cylinderinterior through the end-wall and including a portin said end Wall, aport closure for said'port and movable'into port-open and port-closedpositions, and a Vport closure operator-connected to gui-de the portclosure ink its movement between open and closedpositions, the portclosure operator-consisting of an elongate member extendingsubstantially throughout the surge chamber; means including said atleast one axial passage and the exhaust chamber to withdraw spentelastic uid from the cylinder; port closure operator guide meansincluding a sleeve mounted on the end of the surge chamber, the portclosure operator being mounted to reciprocate in said sleeve; and detentmeans having a member carried by the surge chamber and another member onthe port closure operator, the detent means serving to hold the portclosure operator in one position.

20. In a reciprocating expansion engine: a cylinder; an end wall for oneend of the cylinder; an exhaust chamber at the other end of thecylinder; a piston reciprocably mounted in the cylinder and having atleast one axial passage therethrough; a piston rod secured to the pistonand extending out through sai-d other end of the cylinder and throughthe exhaust chamber; means to admit an elastic fluid to the cylinderthrough the end wall including a port in said end wall, a port closurefor said port and movable into port-open and port-closed positions, anda port closure operator connected to guide the port closure in itsmovement between open and closed positions; means carried by said oneend to guide the port closure operator; means including said at leastone axial p-assage and the exhaust chamber to withdraw spent elasticfluid from the cylinder including a passage closure movable intopassage-open and passage-closed positions and including also a passageclosure operator connected to guide the passage closure in its movementbetween open and closed positions; and guide surfaces provided on thetwo operators, the guide surfaces cooperating to provide at least partof the guide means for the passage closure operator.

21. An expansion engine as in claim 20, in which the last-named guidemeans also includes other mutually cooperable guide surfaces on thepassage closure operator and the piston.

22. In an expansion engine as in claim 21, detent means cooperable withthe port closure operator to hold it in port-open position, and otherdetent means cooperable with the passage closure operator to hold it inpassage-open position.

23. In an expansion engine, a cylinder, an end wall for the cylinder andhaving a port, a closure for the port, ay piston having at least oneaxial passage and reciprocably mounted in the cylinder, a closure forthe axial passage, a closure operator for the port closure, anotherclosure operator for the passage closure, detent means associated withthe port closure operator to hold it in port-open position, other detentmeans associated with the passage closure operator to hold it inpassageopen position, means to disengage the rstnamed detent means andclose the port, and means to disengage said other detent means and closethe passage, said port closing means including a resilient deviceadapted to resist yielding until the port is closed and to yield afterthe port is closed.

24. An expansion engine as in claim 23, in which the resilient deviceembodies means to i9 effect short cut-off and means to effect long cut-01T.

25. An expansion engine as in claim 24, and pressure operated means torender ineffective one of the means to effect cut-off.

26. An expansion engine as in claim 25, in.

which the resilient device is carried by the port closure operator, thefirst-named disengaging means including also a cam surface cooperablewith the resilient device to engage the short cutoi means unless it isrendered ineective by the pressure operated means.

27. An expansion engine as in claim 26, in which the resilient deviceincludes a spring to bias the short cut-off means and another spring tobias the long cut-off means, and in which the pressure operated meansincludes a pressure sensitive bellows enclosing said one of the means toeffect cut-off and means to vary the pressure to which the bellows issensitive.

28. In a reciprocating expansion engine, a cylinder, an inlet surgechamber adjacent one end of the cylinder, an end wall for said one endof the cylinder and separating the surge chamber and the cylinderinterior, an exhaust chamber at the other end of the cylinder, a pistonreciprocably mounted in the cylinder and having at least one axialpassage therethrough, a piston rod secured to the piston and extendingout through said other end of the cylinder, means including said atleast one axial passage and the exhaust chamber to withdraw spentelastic uid from the cylinder, a port in said end Wall, a port closurefor said'port and movable into port-open and portclosed positions, aport closure operator connected to guide the port closure in itsmovement between open and closed positions, detent means cooperable withthe port closure to hold it and the port in port-open position, andmeans to disengage the detent means to effect closure of the portclosure, said disengaging means including a resilient device havingmeans to eiect short cut-oli and means to effect long cut-oi.

29. An expansion engine as in claim 28, in which the resilient device isdisposed in the surge chamber and includes a spring, a bellows deviceencasing the spring, and means alternately to subject the interior ofthe bellows device to surge chamber pressure and to a differentpressure.

30. An expansion engine as in claim 29, in which the last-named meansincludes a valve connected with the surge chamber and with the exhaustchamber and movable to connect the bellows interior with one chamber orthe other.

ROBERT W. HUGHES.

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